0508. Most Frequent Subtree Sum

https://leetcode.com/problems/most-frequent-subtree-sum

Description

Given the root of a binary tree, return the most frequent subtree sum. If there is a tie, return all the values with the highest frequency in any order.

The subtree sum of a node is defined as the sum of all the node values formed by the subtree rooted at that node (including the node itself).

Example 1:

**Input:** root = [5,2,-3]
**Output:** [2,-3,4]

Example 2:

**Input:** root = [5,2,-5]
**Output:** [2]

Constraints:

• The number of nodes in the tree is in the range [1, 104].

• -105 <= Node.val <= 105

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